This invention relates to a power-supply circuit for energizing a load and comprises two input terminals for the application of an input voltage. Coupled to the input terminals are a rectifier, a first capacitor having terminals for the connection of the load, a first transistor switch having a control electrode, and second transistor switch for turning off the first transistor switch when the rectified input voltage exceeds a specific value.
Such a circuit is suitable for energizing a load with different input voltages. Such a circuit is particularly suitable for use in a dryshaver in which the circuit is utilized for energizing the motor. This enables the shaver to be used with different mains voltages available in various countries without the need for an adaptor or switching over.
Such a circuit is known from U.S. Pat. No. 4,001,668. In this circuit the first capacitor is maintained at an average constant voltage in that both during the rising edge and the falling edge of the rectified input voltage the first capacitor is recharged to the value of the rectified input voltage defined by the second transistor switch. A drawback of this circuit is that it generates a comparatively large amount of spurious radiation. This is because during the falling edge of the rectified input voltage the first transistor switch is turned on at the value of the input voltage defined by the second transistor switch, while at this instant the voltage across the first capacitor is lower than this value. As a result of this, the first capacitor is charged with a comparatively large charging current, so that the voltage across this capacitor increases stepwise to the value of the rectified input voltage defined by the second transistor switch.